65. Covalent Bonding(11)- sp3d Hybridization.

In the last few posts, we studied about the most common types of hybridization namely -sp3, sp2, and sp hybridization. These are exhibited predominantly by elements in the second period of the periodic table(e.g. Carbon, Oxygen, Nitrogen, Beryllium, etc).

 However, the concept of hybridization can be extended to the p- block elements(e.g.- Suphur, Phosphorous, Iodine etc ) as well.The p-block elements have vacant d-orbitals of similar energy (NOT SAME) , as that of valence s- and p-orbitals. Thus, the electrons from the s-orbital can be excited to the vacant d-orbitals. Then the s, p and d orbitals mix to form sp³d, sp3d² or sp³d³  hybrid orbitals.These type of hybridizations are different than the earlier ones as they involve the vacant d-orbitals.

We will discuss each of these hybridizations this post onwards.

sp³d hybridization.

The process of mixing of one s- orbital ,three p- orbitals and one d-orbital in an atom to form five sp³ d hybrid orbitals of equivalent energy is called sp³ d hybridization.

EXAMPLE 1 – PHOSPHOROUS PENTACHLORIDE (PCl₅ )

Phosphorous is a p-block element (Group 15, non-metal).It is the central atom in PCl₅  and  is sp³d hybridized.

Phosphorous (15) 1s² 2s² 2p⁶ 3s² 3p³ → Ground state. 

One s – electron promoted to d orbital → 1s² 2s² 2p⁶ 3s¹ 3p³ 3d¹.

The 3s , three 3p and one 3d orbitals hybridize to form sp³d hybridization. The molecule is then formed with 5 chlorine atoms.

Phosphorous pentachloride has a trigonal bipyramidal geometry with 90º and 120º bond angles. The angle between the equatorial chorine atoms is 120º and that between the equatorial and axial chorine atoms is 90º as shown in the figure below – 

What happens when a lone pair is involved in sp³d hybridization? How does the geometry change? Let us study that with an example –

EXAMPLE 2 – SULFUR TETRAFLUORIDE (SF₄).

Sulphur too is a p-block element as it has it’s valence electrons in the 3p orbital. It has vacant 3d orbitals ,to which an 3s electron can be promoted easily (as the energy difference between 3s, 3p and 3d is not much ) to undergo sp³d hybridization.

Sulphur  1s² 2s² 2p⁶ 3s² 3p⁴ → Ground state.

Sulphur 1s² 2s² 2p⁶ 3s¹ 3p⁴ 3d¹ → Excited state.

The 3s , three 3p and one 3d orbitals hybridize to form sp³d hybridization. The molecule is then formed with 4 chlorine atoms.

The lone pair of electron , needs more space and so it pushes the other electrons. This gives the molecule a seesaw shape .

We continue our discussion about hybridization in our next post.Till then,

Be a perpetual student of life and keep learning …

Good Day!